I. Field of the Invention
The present invention relates to a method for exchanging reliable information between nodes in an ad hoc network.
II. Description of Related Art
On an average day, hundreds of people are killed and thousands injured in automotive accidents. This, in turn, results in a huge expenditure of health care dollars for treating those injured in such automotive accidents.
Many automotive accidents, however, are preventable if the vehicle driver is warned of a hazardous driving condition, or the vehicle itself reacts automatically to such a hazardous condition. For example, a driver may cause a chain reaction accident by rapidly applying his or her brakes in order to avoid collision with a deer or other animal. The drivers behind the vehicle about to strike the animal, however, are unable to brake sufficiently rapidly in order to avoid an accident thus resulting in a chain reaction accident. However, such an accident may be theoretically prevented, or at least the injuries and/or damages minimized, if the driver and/or vehicle potentially involved in the accident are able to react sufficiently rapidly to hazardous driving conditions in the vicinity.
For that reason, dedicated short range communications (DSRC) have been proposed to permit communication between automotive vehicles as well as vehicles and infrastructure for safety communications. Indeed, the federal government in the United States has allotted 75 MHz of the wireless spectrum in the 5.9 GHz range for such communications.
In managing the wireless communication between different vehicles, as well as between vehicles and infrastructure, authentication that the messages received by any particular automotive vehicle are trustworthy and constitute reliable information is paramount. Without such authentication, the vehicles may receive wireless communication from parties who intentionally transmit incorrect information for whatever private purpose, as well as vehicles that, through malfunction, transmit incorrect information. Without authentication of the reliability of the received messages, unsafe traffic conditions, traffic congestion, etc. may result.
In order to enable automotive vehicles to communicate between themselves and optionally infrastructure, it has been previously proposed to form a vehicle ad hoc network (VANET) with the automotive vehicles that are within the range of interest for the automotive vehicle. Such vehicles would then communicate amongst themselves within the network providing safety information, such as the status or status of operation of each vehicle in the network as well as infrastructure adjacent the road.
In order to ensure the authenticity of the messages received within the network, it has been previously proposed to use public key infrastructure (PKI) encryption of the messages transmitted over the network. In such a PKI encryption system, a certificate authority, such as a governmental body, distributes a public key to all the vehicles or nodes within the network. The certificate authority then also provides a signature encrypted with a private key to each node or vehicle and in which the signature is unique to that particular vehicle. For example, the PKI encrypted certificate authority signature may be bound to the vehicle identification number (VIN), license plate, and/or the like. The certificate authority may also revoke the encrypted signature for any particular vehicle if it is determined that that vehicle no longer transmits trustworthy or reliable information.
In practice, the vehicles in the node transmit a message, which includes not only the vehicle identification but potentially safety information, together with the encrypted certificate authority signature. Upon receipt of that message by another vehicle, the other vehicle utilizes the public key of the certificate authority to decrypt the received certificate authority signature. That decrypted signature is then compared to a result of a hash function applied to the received message. If a match results, both the accuracy of the message is authenticated as well as the signature of the signature certificate authority thus verifying that the information received is valid. Otherwise, the received message is discarded and ignored.
The certificate authority, of course, retains the ability to revoke its encrypted certificate authority signature from any particular vehicle at any time in the event that that vehicle begins to transmit unreliable information.
While the PKI encryption method for authenticating received messages in an ad hoc network provides sufficient security for the authenticity of the messages received in the ad hoc network, the security certificate authority signature which accompanies the messages transmitted in the network is several times the size of the actual message itself. This, together with the repetitive description of the certificate authority signature for each message, results in higher computational cost and bandwidth requirements, particularly where there are numerous vehicles in the ad hoc network.